Step 1: Prepare the Toppings

1. Heat the butter and olive oil in a small skillet over medium heat.
2. Add the sliced onions and sauté for 6-8 minutes until softened and golden brown.
3. Toss in the sliced jalapeños and cook for 2-3 more minutes. Remove from heat and set aside.

Step 2: Cook the Patties

1. Divide the ground beef into 4 equal portions and loosely shape them into balls. Do not overwork the meat.
2. Heat the cast iron skillet or griddle over medium-high heat until very hot.
3. Place the beef balls on the skillet and smash them flat using a spatula (use parchment paper between the spatula and meat to prevent sticking).
4. Season with salt and pepper, and cook for 2-3 minutes until crispy. Flip, add a slice of cheese to each patty, and cook for another 1-2 minutes.

Step 3: Assemble the Burgers

1. Toast the burger buns on the skillet until lightly golden.
2. Spread chipotle mayo or your preferred sauce on the bottom bun.
3. Add the cooked patty with melted cheese, then pile on the sautéed onions and jalapeños.
4. Top with any additional desired toppings, then crown with the top bun.